Two systems of making •ice are now used, the compressor and the absorption systems, the former the more generally used. The first step is the compression of the anhydrous ammonia (that is, ammonia which contains no water) by means of a steam pump, a pressure of from 125 to 175 pounds per square inch being ex erted. This raises the boiling point of the ammonia. This pressure heats the ammonia and it gasifies as released. The next step is to reduce the gas to a liquid state by passing the ammonia through pipes which are in contact with the cold water or some other cold sub stance. By the condensation process the heat is greatly reduced and it loses theoretically all the heat it gained by compression. Thus the temperature of the ammonia falls to or 10° F., and when it is circulated around tanks or cans containing water, the water freezes in a few hours. A good ammonia ice-machine will produce 30 pounds of ice with one pound of coal.
In the absorption process aqua ammonia is first converted into gas by the application of heat which raises the pressure to from 120 to 160 pounds per square inch. The ammonia is then reduced to liquid form by being passed through pipes in contact with cold water. The ammonia is then changed from a liquid to a gaseous form by expansion, the methods being the same as in the compressor system. The ex pansion draws out any heat in the gas, which, as it passes through the pipes in contact with the water to be frozen, absorbs the heat from them till they are of a like temperature.
A large portion of the ice manufactured in the United States is produced by the can sys tem or the plate system. In making ice by the can system the water is first boiled and allowed to settle, in order to free the ice from any foreign substances and to reduce it to the greatest possible degree of purity. The water is then distilled, boiled again and run through three kinds of filters. A series of tanks, con taining a strong solution of brine, is placed un der the freezing room and through this brine run the pipes containing the liquefied ammonia gas. Into the tanks containing the brine are submerged the cans holding the water to be frozen. The ammonia in the pipes is expanded into gas as it passes into the brine and absorbs enough heat from the brine and water to form the water in the can into ice. The whole proc ess requires from 20 to 66 hours, according to the size and weight of the blocks of ice and to the temperature of the brine. The can is then raised from the tanks by means of a hoist and dipped into a well of warm water to loosen the contents. The blocks produced weigh from 50 to 400 pounds.
The production of ice by the plate system is much slower and more cumbersome. In this process the tank contains the water to be frozen and into it is placed a hollow iron plate holding the coils of pipe filled with the freezing medium.
Thus the ice is formed on the outside of the iron plate, is taken out and removed and is then ready, for use. The mechanism of an ice plant consists mainly of a steam-boiler, feed water conveniences, an oil-separator or high pressure trap for removing the oil that collects in the ammonia, a steam-condenser, feed-water pump, an ice-machine, freezing tanks or cans and a cooling tower, where the heated water may be brought in contact with the atmosphere to quickly reduce its temperature.
The rapid growth of the artificial ice in dustry is most eloquently shown by the census figures. During the period between 1870 and 1880, the number of establishments increased from four to 35, and the production from a quarter million dollars worth to over half a mil lion. During the next decade the number of factories increased from 35 to 222, and the production rose to almost $5,000,000 worth. Ten years later in 1900 the census records 787 es tablishments, with a capital of nearly$40,000, $14 000, and an annual product of nearly ,000, 000 worth of artificial ice, most of this manu facture being in the Middle or Central States of the country. By 1905 the factories had •in creased to 1,320, the capital to $66,600,000, and the industry gave employment to over 12,000 people, receiving $5,550,000 in wages and salaries. The total production for the previous year was worth $23,790,000. In 1910 there were 2,004 factories, mostly capitalized between $20,000 and $100,000, and the production was valued at $42,453,000, while the wage earners in creased to 16,000. In 1916 a conservative esti mate places the total of factories at 2,500, and their production at $55,000,000 annually. Pennsylvania is the leading State in the indus try, with 200 factories and 11.2 per cent of the country's production. Texas and New York each are credited with 8.9 per cent of the total production, but Texas has 200 factories to about 100 for New York State. Ohio, Indiana and Tennessee are the next States in the industry.
Strange to say the largest item of expense in the artificial ice industry is neither labor nor materials, as in most other manufactures. The material being water costs little and the ma chinery does the work. The great item of ex pense is coal, to produce the heat to expand the steam and run the compressor ice-machines.
The cost of producing a ton of ice averages throughout the country for all seasons of. the year, between $1.00 and $1.50; the average price to the wholesaler ranges from $2 to $225; and the retail prices range from 15 to 40 cents per hundredweight according to the season. The changes and improvements in the methods of producing artificial ice have so reduced the cost of manufacture that it now competes with the natural product. See REFRIGERATION AND REFRIGERATING MACHINERY.